Setback charging condenser



Unitd 'States Y Y `2,934,017 sErnAcn CHARGmG CONDENSER Alexander Ellett, River Forest, Ill., assignor to the United States of America as represented by the Secretary of the Army 1" Application April 26, 1""951, serial N0. 6ss,4s4

js claims. (camz-10.2)

This invention relates to fuzes for ammunition, and more particularly to fuzes f the piezoelectric condenser type It is an object of this invention to provide a fuzehaving simple reliable electrical means for detonating an explosive train. A

It is an important object of this invention to provide a fuze having a voltage generator'responsive to set-back. Another object of this invention is the provision in a fuze having a voltage generator, of means for maintaining the voltage developed for the duration of the ight.

of the missile. t `It is a further object of this invention to provide in an electrically actuated fuze afcondenser charged upon set-back. p

A further object of this inventionis the provision in an electrically actuatedffuzeof a condenser discharge` able only upon contact with the target.

Another object of this invention is toprovide in a fuze,

meansby which a normally' closed microswitch is opened in response to a predetermined acceleration.

arent Thev condenser is charged by stressing the piezoelectric f material.` The fuze detonates upon contactwith the target when the condenser discharges.

The invention is disclosedv in two embodiments. In the first, the means for stressing the piezoelectric material takes the form of a rotatable, eccentrically mounted weight. The weight hasa cam surface designed to wedge" a shell incorporating a first embodiment of the invention;

Fig. 2 is a longitudinal section of a fuze4 disclosing a second embodiment of the invention.

The structurel described in the following paragraph is common to the fuzes disclosed in Figs. 1 and 2. Similar reference characters indicate identical parts in the two figures. There is shown an explosive shell casing 1 containing an explosive charge 2, the casing being internally threaded at 3 for the attachment of a fuze assembly.

- posite end, a first cylindric axially extending passage 9 Yet another objectpof this invention is to provide in an electrically actuated fuze a condenser of the type which is' formed by sandwiching piezoelectric material between electrodes.

It is still another object of `this invention to provide means in an electrically actuatedV fuze for stressing the piezoelectric material in a condenser to charge the condenser.

Itis an additional object of this invention to provide means in an electrically actuated fuze for Autilizing setback forces to stress a piezoelectric wafer.

Otherr objects, and the manner inlwhich they are attained, will appear from the following description.

The structures described in thisapplication are calculated to take advantage of certain peculiar characteristics of piezoelectric materials. If a wafer of this material is Vprovided with electrodes on the proper faces and is then stressed (as by compression along an appropri- 'ate axis) while theelectrodes are open circuited, a voltage proportional to the stress Willbc induced between the electrodes. This phenomenon is reversible; on removing the stress, the voltage drops to zero. If, in the condition in which the wafer is under stress andthe circuit open, the electrodes are suddenly short circuited, current will ow between the electrodes.A If the electrodes are short circuitedV `during an entire stressing cycle no The fuze assembly consists of a fuze body 4 having internal -threads 5 at one end for receiving both a-retaining ring 6 and a booster cup 7 containing the booster charge S. The uze body at this end alsopis provided with external threads for mating with the internal threads 3 of the shell casing. The fuze body includes at its `op formed with a seat 11 and a second cylindric axially extending passage 12 of smaller diameter communicating with the rst passage. The second passage 12 communicates with a fuze chamber 13 adapted to accommodate the fuze actuating mechanism. This chamber has aforward wall 14 and is divided'by shoulder 15 into a for- Yward portion and a rear portion ofv relatively larger diameter. Slidably mounted in passages 9 and 12 is a ring pin 16 having ahead portion 17 and an integral pin 18. The head portion 17 is slidably mounted in passage 9, while the pin is slidably mounted in passage 12. The pin extends entirely through passage 12 and voltage appears between them. The charge is transferred from one electrode to the other, and back again when the stress is removed.

Broadly, the invention involves the provision in a fuze of a voltage generator actuated in response to set-back, in which the voltage is maintained at an elevated level during flight of the' missile, and only discharged in response to impact with the target.

More specilically, the invention involves the provision in a fuze of means-for charging a condenser formed of piezoelectric material Usandwiched between electrodes.

projects into the forward portion of chamber 13. A coil spring 19 guided by pin 1S is located inpassage 9 between seat 11v and the head 16 of the ring pin. This spring biases the tiring pin t`o a forward position. Clos ing the outer extremity of passage 9 is a retaining disc 21 with which thespring-biased tiring pin is held in contact. In chamber 13 and threadably .secured to the forward wall 14 are, screw members 22 and 23 having insulating sleeves Z4 and ZS-mounted respectively thereon.V

Contact members Z6 and 27'are mounted respectively on screw members 22 and 23 but insulated therefrom by the aforesaid insulating sleeves. The contact members 26 and 27 have contact'points 28 and 29 respectively, in axial alignment with each other and vwith the pin 18 of the tiring pin. l

Referringv now particularly to Fig. l, there is located in therear portion of cylindricgY chamber 13 a cup-shaped insulating member 31 which isxed in position between* retaining ring 5 and the insulating disc 34 which abuis shoulder 15. The cup-shaped insulating member llhas cylindricalrwall 32 and bottom wall 33. Thercup-'shaped insulatingrmember 3K1 and the insulating disc 34";form an insulated ,chamber within which a voltage Vgenerator (generally indicated at B) `is located; In the bottom wall 33 of the cup-shaped insulating memberisa cylindrical recess 35 opening into the insulated chamben -This Patented Apr. 26, 1960V recess 35 -has a longitudinal axis common with the axis of the fuze body when the insulating member 31 is in assembled position. In the bottom of recess 35 is a shallow contact plate recess 36. Positioned in recess 36 is ,a `Contact. plate 37. Contact plate 37 is of greater depth than recess 36 and therefore projects somewhat into recess 35. A piezoelectric wafer 38 providedl with electrodes 39 and 41 on opposite'sides thereof is positioned partly .within recess 35. Electrode 41 is in engagement with rcontact plate 37. Supported above the electrode 39 is a weight member 42 rotatable on shr-.ft 43. The weight member has a cam surface 44 which is normally in contact with electrode 39. The shaft 43 is positioned at a right angle to the longitudinal axis of the fuze body and lies at one side of this axis. On the rearward side of the bottom wall 33 and axially aligned with the recess 35 is a detonator recess 45 formed by wall 46 depending from bottom wall 33. Located in the detonator recess 45 is an element of an explosive train, a detonating charge 47, in which is embedded a squib ork initiator 48. Y

The actuating circuit is arranged as follows: Lead 49 passcss through a portion of bottom wall `33 of the cupshaped insulating member to connect to contact plate 37. At its other end lead 49 is connected toone end of the squib 48. Lead 51 is connected to the opposite end of the squib, then passes entirely through bottom wall 33 at 52, through Adisc 34 at 53, and is then connected to contact member 26. A third lead 54 is connected to switch member 27, passes through disc 34 at 55, and'then is connected to electrode 39.

As stated above, the eccentricV weight 42 is disposed above the piezoelectric wafer 38 with its cam surface` normally in contact with the electrode 39. This eccentric weight is so shaped and proportioned that acceleration in the direction of arrow A causes the weight to rotate in a counter-clockwise direction on shaft 43 to place the wafer under compression. A known accelerating force produces a definite displacement of the weight and if the cam contour of the weight is related to the angle of friction, the wafer may be locked in compression. It has been found that if the angle of the cam surface presented to the wafer at the selected accelerating force is in the neighborhood of tive degrees, the

weight will lock against the wafer.

The embodiment disclosed in Figure l operates as follows: The weight member 42 rotates on set-back stressing the wafer. Cam face 44 locks weight 42 against electrode 39 holding the wafer in stressed condition. The stressed condition of the wafer, and hence the voltage between the electrodes, is maintained throughout the Hight of the projectile. The electrodes are open circuited since contact points 28 and 29 are Vnot in engagement. Upon striking the target the tiring pin 16Yis driven backward overcoming the resistance of spring 19 and forcing contact point 28 into engagement with contact point 29. Current then iows through leads 54, 51, and 49 actuating the initiator 48 and the detonator 47. i f Referring now' to Fig. 2, in the rear portion of chamber 13 a'cup-shaped insulating member 61 forms, with its cylindrical wall 62, bottom wall 63, and the insulating mounting disc 64, an insulated chamber. A voltage generator, generally indicated at C, is mounted partly within said chamber and partly on said mounting disc in the forward portion of chamber 13. In the bottom Wall 63 of the cup-shaped insulating member is a cylindrical recess 65 opening into the insulated chamber. This recess 65 has a longitudinal axis aligned with the axis of the fuze body when the insulating member 61 is in assembled position. In the bottom of recess 65 is a Contact plate recess 66. Positioned in recess 66 is a contact plate 67. A piezoelectric element 68 is "provided with electrodes 69 and71 on opposite sides thereof and is positioned in recess 65. Electrode 71 extends into 4 plate recess 66 and abuts contact plate 67. A guide recess 73 formed by cylindrical wall 74 depending from mounting disc 64 opens into the insulated chamber. A cylindrical weight 72 is slidably mounted in guide recess 73 in contact with electrode 69. The axes of the guide recess and cylindrical weight coincide with the axis of the fuze body. A normally closed shortening microswitch, indicated generally at 75, is securedon mounting disc 64 in the forward portion of chamber 13. Mounting screw 76 is xed to the mounting disc 64. Contact members 77 and 78 are tixed at one end to the screw -.76'and insulated therefrom and from each other by insulating sleeve 79.

. Contact members 77 and 78 have contact points 81 and 82, thereon respectively, in alignment with and contacting each other. Contact member 78 has a forwardly extending lug 83 at its outer extremity. A weight 84 is rotatably mounted on shaft 85 in contact with lug 83. The axis of shaft 85 is perpendicular to and lies at one side of the longitudinal axis of the fuze body. A spring latch 86 fixed to mounting disc 64 holds weight 84 in a forward position. On the rearward side of the bottom wall 63, and axially aligned with the recess 65, is a detonator vrecess 87. As in the structure shown in Fig. l, a detonating charge 88, the first element of an explosive train,is located inl recess 87 and has embedded in its a squib or initiator 89."

A shorting circuit is provided in this embodiment as follows: A lead 91, passingthrough disc 64 at 92, connects contact plate 67 with contact member 77 of the normally closed microswitch 75. Lead 93 connects contact member 78 of the microswitch with electrode 69 of the piezoelectric element.

The actuating circuitv is arranged as follows: A lead 94 is connected to one end of initiator 89, passes through bottom wall 63 at 95, through disc 64 at 96, and is then lconnected to contact member 27. Lead 97 is connected at one end to contact member 26, passes through disc 64 at 98, and is connected at the other end to electrode 69, Contact plate 67 is connected `to initiator 89 by lead 99.

The embodiment of Fig. 2 operates in this manner: On set-back the weight 72 slides rearward placing the piezof electric wafer under compression. No voltage appears between the electrodes since they are short circuited through normally closed lmicroswitch 75. At some high point in compression the inertial forces become suicient to rotate weight 84 in a counter-clockwise direction over coming spring latch 86 (note dotted line position 101). In rotating, the weight moves lug 83 rearwardly and thus breaks the contactfpoints of the microswitch. The weight is now iixed in the rearward position by the latch S6 and, consequently, the microswitch is held open. As the acceleration of the missile drops, the stress on the piezoelectric wafer is gradually relieved and, since some maldistribution of charge occurred when the electrodes were shorted, a voltage now appears between the electrodes. The two electrodes and the separating piezoelectric material constitute a condenser, and under the conditions described above, we have a charged condenser. Upon striking the target the tiring pin 16 is driven rearward against spring 19 forcing contact point 28 into engagement with contact point 29. The piezoelectric wafer n ow discharges through leads 99, 94 and 97 actuating the initiator 89 and the detonator 88.

Having described my invention and the advantages thereof, it will be obvious to those skilled in the art that various modieations and changes may be made in the embodiments disclosed above without departing from the It is my intention to and a normally open switch in said actuating circuit adapted to close on impact for discharging said voltage through said actuating circuit and said squib. I

2. In a fuze for an explosive projectile, an electric squib for initiating an explosive train, piezoelectric means for energizing said squib comprising a Wafer having electrodes at opposite faces thereof, set-back responsive means including a rotatably'mountedfweight member having a cam surface thereon, said cam surface being in contact with said Wafer and shaped to stress said wafer upon rotation at set-back to developand maintain a predetermined voltage between said electrodes by wedging against saidwafenin stressed condition, said voltagebeing maintained` between said electrodes during flight of said projectile, and impact responsive means `including contacts for discharging said electrodes to energize said squib.

3. .In a fuze for an explosive device, an electric squib for initiating an explosive train, piezoelectric means for energizing said squib including a wafer having electrodes at opposite faces thereof, set-back responsive means including rst and second weight members,` said rst weight member slidably positioned in contact with said wafer to stress said wafer upon set-back and thus develop a predetermined voltage, a shorting circuit including a normally closed switch connecting said electrodes, said second Weight member rotatably mounted in contact with said switch to open same in'response to set-back, spring means to delay movement of said second Weight member, an actuating circuit including said squib, and a normally open switch in said actuating circuit adapted to close onimpact for discharging said voltage through said actuating circuit and said squib. V

4. In an explosive projectile, electrical fuze means including an actuating circuit, a Vpiezoelectric wafer having electrodes at either side thereof in said circuit, said wafer Y in contact with and positioned between fixed and movable Vmembers, said movable member responsive to set-back to stress said wafer and thereby develop a predetermined voltage between said electrodes, said voltage being maintainedtbetween said electrodes during the ight of said projectile, an electric squib and a normally open switch in said circuit, plunger means in the nosel of said projectile movable to close said switch upon contact with a target, said voltage discharging throughsaid squib when said switch closes.

5. In an explosive projectile, electrical fuze means including an actuating circuit a piezoelectric wafer having electrodes at either side thereof in said circuit, said wafer in contact with and positioned between a fixed member and a'movably mounted compression member, said cornpression member responsive to set-back to stress said wafer References Cited in the le of this-patent vUNITED STATES PATENTS 'Y Ruhlemann May v17, i932 Hudson Sept. 25, 1956 

